A speaker refers to a device that includes a voice coil and a vibration plate which are arranged in a magnetic field, and generates compressional waves as sound waves in the air by vibrating the vibration plate using a Lorentz force which is generated in the voice coil by an electrical signal. Conventionally, electrodynamic loudspeakers have been widely used, which vibrate a cone-shaped vibration plate using a voice coil wound in a cylindrical shape. Recently, however, the use of flat speakers capable of reducing a speaker installation space has increased, with the reduction in size and thickness of display devices or mobile terminals in which audio systems mounted.
The flat speaker generally includes a pair of magnetic bodies, a voice coil plate and a vibration plate. The pair of magnetic bodies are arranged with a predetermined space provided therebetween, and thus form a magnetic space for a magnetic field therebetween, the voice coil plate is disposed in the magnetic field, and the vibration plate is vertically coupled to an upper edge of the voice coil plate, and vibrated by a motion of the voice coil plate. The voice coil plate includes a plate or film-shaped base substrate and a voice coil pattern. The voice coil pattern is wound in a track shape or printed in a similar manner on the surface of the base substrate.
In order to generate a higher electromagnetic force in a limited-area voice coil plate, the integration density of the voice coil pattern must be increased. However, there is a limitation in increasing the number of windings by reducing the line width of the coil pattern, due to an increase of resistance. In order to overcome such a limitation, various techniques have been developed. According to one of the techniques, voice coil patterns may be formed on one or both surfaces of several base substrates, and the base substrates may be vertically stacked. Further, voice coil patterns of two layers adjacent to each other may be connected in series to each other in order to acquire an appropriate resistance value depending on the design intention in a multilayer voice coil plate.
According to the related arts, however, the shapes or lengths of the voice coil patterns are different from each other, the shapes of the voice coil patterns including the positions of via holes for connecting the respective layers of the voice coil patterns. Therefore, the voice coil patterns need to be designed for the respective layers. When the resistance value is changed by a difference in shape or length between the voice coil patterns at each of the layers, it is more difficult to adjust the composite resistance value of the entire voice coil plate to the target resistance value depending on the design intention.
Furthermore, the stacked structures according to the related arts require one base substrate for each layer or at least one base substrate for each two layers of the multilayer voice coil patterns. Thus, the thickness and mass of the voice coil plate are inevitably increased to thereby degrade the effect obtained by increasing the number of coil windings.